I recently purchased 6 Topre thermochromic spacebars from hidden lab and they all have issues staying seated in the Topre spacebar stabs. The stabilizer rectangles on the spacebars appear to look fine and the bars themselves aren't warped, but pressing on the edges of the spacebar a few times always unseats the spacebar from the stabilizer. I tested this on several Topre boards that I have along with a co-workers to find that the issue happens on all of them. I've reached out to Hidden Lab in an attempt to determine if maybe they can send me new spacebars. Here is a link to a video demonstrating the problem on three different Topre boards. Sometimes, it seems no matter how I press on the spacebar it won't actually seat in the stabilizer and other times I manage to get it in, but then after a few presses on the edge it pops right back out. I posted this on /r/mk already, but it fell into the abyss.

Try cutting a small patch from a sandwich bag, laying it atop the stab stem, and then installing the spacebar.

Just tried. It does in fact work around the issue although I'm not particularly pleased with a bandaid solution. The pieces of plastic I cut were just large enough so that now I hear a plastic scratching sound when the edges rub up against something as the spacebar is pressed.